This invention pertains to a film projection system using cartridges of film to be loaded into a projector having a viewing screen for display of images of the film from the cartridges therein. This invention particularly pertains to such a system in which the insertion of the cartridge into the system serves to establish a predetermined focal length in the lens system of the projector to provide repeatable accurate automatic focusing among a number of such cartridges used with a single projector or when using one cartridge with a number of such projectors.
Heretofore, film projection viewing systems, such as microfilm reader systems, have employed projectors into which cartridges of film could be disposed but, upon insertion of each cartridge into the projector, follow-on focusing of the projector can be expected to be required from one cartridge to the next. In addition, it has been the rule that the projector should contain the microfilm transport apparatus, such as means for tensioning the film as it arrives at a point for projection, as so to leave the cartridge in a relatively simple state of construction involving the barest of elements therein.
It has been observed that there are substantial advantages to be obtained by providing the herein disclosed system as will be pointed out further below.